Grate Bar and Grate for a Step-Grate Stocker with Directed Air Combustion

ABSTRACT

A grate bar and a grate for stepped-grate furnace stoker with directed-air combustion. Its principle application is in the field of furnaces for waste conversion units. The bar includes a flat part, whose top surface receives the incinerated elements, and that extends into two rear and front ends each forming a return that acts as a support point for the bar. It also includes a longitudinal projection under the flat part, extending at least partially between the rear and front ends. At least one wing is positioned under the flat part, on a first side of the longitudinal projection. In a characteristic manner, this wing has at least one lateral hollow-out which, together with the lateral hollow-out of a wing of a neighbouring bar, forms a passage for channeling air up to the front end of the bar.

The subject of this present invention is a grate bar and a grate for a stepped-grate furnace stoker with directed-air combustion. Its principal application is in the field of furnaces for waste conversion units, such as common refuse, industrial, domestic, or hospital wastes, water treatment sludges, or flour for example.

The question of waste incineration has long been a problem in our societies, which are producing more and more of it. The furnaces which have actually been designed for waste incineration have existed for many years, and have undergone constant development up to the present time. These include known furnaces such as grate furnaces, roller-hearth furnaces or fluidised-bed furnaces, for example, in which the waste materials are emptied through a hopper onto a conveyor composed of mobile steps that blend and push the waste materials forward into the combustion chambers. These furnaces thus allow the combustion of the waste materials, and therefore a reduction in the production of pollution.

Nowadays, we speak of the recovery or re-use of the waste materials. In fact, we no longer seek to make it disappear or to reduce its volume significantly, but also to recover the energy that comes from the combustion process.

In a recovery unit, the furnace is the part in which the waste materials are dried and where their combustible content is oxidised. An efficient furnace should be designed so that the waste materials are well distributed over the combustion bed, and are correctly blended. This blending is used to bring the waste materials into contact with the hot air coming from the furnace in order to dry them, to distil the volatile substances and to break down the products into simple molecules that finish by attaining their ignition temperature.

The quality of the combustion is linked mainly to oxygen content, which must be sufficient, to the temperature, which must be high, to the controlled turbulence which must be sufficient for good combustion while avoiding the releases of composed of flying ash, and to an adequate time of presence of the waste materials on the grate.

Most of the known grates include bars whose main section has the shape of an inverted “U”, meaning a flat part and two lateral legs, which are assembled so as to form a mobile step-feed, in which some bars move in limited translation in relation to the others, in a manner that moves the particles forward and empties them out. One of the drawbacks of this type of bar is that the path that the particles must travel along the legs of the bars, before they are completely emptied out below these bars, is a long one. It corresponds in fact to the length of the legs of the bar. One of the consequences is therefore that the particles are heated for longer and are liable to stick on, under or between the bars. The progressive accumulation, between and under the bars, of the refractory materials can then, in particular, cause the shuttle motion of the bars to be paralysed. The amplification of the separations between the bars also contributes to blocking the movements of the grate and increases the difficulties of adjusting the combustion. This can require halting production in order to clean or change one or more bars, as a result of mechanical wear.

We know of some grates whose bars have a main section, in the shape of a “T”, meaning with a flat part, and a longitudinal part projecting below the flat part. These bars limit the aforementioned drawback of the bars whose main section is in the shape of an inverted “U”, since the path traveled by the particles being removed between the bars corresponds to the thickness of the flat part, and therefore is shorter.

However, there is also the important problem of cooling. This problem arises from the nature of the products to be treated. In fact, waste materials such as hospital or industrial waste give rise to a very high combustion temperature. Air circulation must therefore be provided, not only to allow cooling of the bars but also to activate the combustion. In general, each bar has its own air circulation path that runs below it, independently of the other bars.

The problem that then arises is therefore to arrange for effective air circulation, in order to allow cooling while still activating the combustion, and to guarantee the relative movement of the bars for correct removal of the particles.

The purpose of the invention is therefore to provide a solution to the aforementioned problems, amongst others.

According to a first aspect, the invention therefore relates to a grate bar for the firebox of an incineration furnace. The bar includes a flat part whose top surface is intended to receive the incinerated elements and that extends into a rear end and a front end, each forming a return that acts as a support point for the bar. The bar also includes a longitudinal projection located under the flat part, and that extends at least partially between the rear and front ends of the bar. At least one wing is positioned under the flat part, on a first side of the longitudinal projection.

In a characteristic manner, this wing positioned under the flat part is provided with at least one lateral hollow-out which, together with the lateral hollow-out of a wing of a first neighbouring bar, forms a passage for channelling the air up to the front end of the bar.

Thus, the oxidising air is advantageously channelled toward the front end of the bar. We thus achieve directed-air combustion.

In a first implementation variant, the bar of the invention includes at least one second wing positioned under the flat part, on a second side of the longitudinal projection. This second wing is provided with a lateral hollow-out which, together with the lateral hollow-out of a wing of a second neighbouring bar, forms a second passage for channelling the air up to the front end of the bar.

The bar preferably includes a multiplicity of wings distributed under the flat part, along the longitudinal projection, on a first side or on each side of this longitudinal projection. These wings are provided with respective lateral hollow-outs which, together with the respective lateral hollow-outs in the wings of the neighbouring bar or bars (9, 13), form passages. In their turn, on the first or on each side of the longitudinal projection, these passages form a channel for guiding the air up to the front end of the bar.

In a second variant, possibly in combination with the first, the passages are outlined at the top at least partially by the bottom surface of the flat part, so that the channelled air runs just below this flat part.

In a third variant, possibly in combination with one or more of any of the previous variants, the bar includes at least one angled cutting element located under the flat part, on a first side of the longitudinal projection.

Alternatively, the bar includes a multiplicity of angled cutting element distributed under the flat part, on a first side or on each side of the longitudinal projection.

Preferably, in one or other of these variants, each of these angled cutting elements is located firstly against the bottom surface of the flat part and perpendicularly to this bottom surface, and secondly against one or other side of the longitudinal projection and perpendicularly to this side.

In a fourth variant, possibly in combination with one or more of any of the previous variants, the base of the front end of the bar has an attack angle α that is greater than 0°.

Preferably, this attack angle α is between 2° and 10°. Preferably still, this attack angle α is more-or-less equal to 3°.

In another variant, possibly in combination with one or more of any of the previous variants, the front end of the flat part is provided, on at least one of the sides of the longitudinal projection, with a fin for redirection of the air coming from the passage or passages formed by the lateral hollow-outs, to at least one channel located in the top part of the front end of the bar.

Preferably, the channel starts at the bottom surface of the flat part and perpendicularly to the latter, and opens out onto the top of the top surface of the flat part, parallel to the latter.

According to a second aspect, the invention also relates to a grate for the firebox of an incineration furnace that includes at least one bar according to the first aspect of the invention presented above.

In an implementation variant, the grate includes at least one group of three bars according to the first aspect of the invention presented above, with the central bar in this group being mobile in relation to the two lateral bars in the group.

Preferably, the bars in at least one of the groups are assembled by means of a dowelling or pinning technique that locks the two lateral bars in relation to each other, and that leaves the central bar free in translation, between two extreme positions, in relation to the two lateral bars.

The invention therefore advantageously allows the formation, under the grate, of channels that direct the air running under the bars of this grate. The formation of these channels, and therefore the advantageous circulation of the air under a bar thus depends on the juxtaposition of this bar with the adjoining bars. This better circulation of air cools the assembly while also favouring and activating the combustion, since the oxidising air is channelled toward the front end of the bar.

The shape, the position and the number of wings combine to accelerate cooling of the bar from below.

The invention also advantageously brings about a better elimination of the particles that accumulate between the bars. This advantage is in particular achieved by a short removal path between each bar, due in particular to the structure of a flat part, and a longitudinal projection under this flat part that provides the assembly with a main section, in the shape of a “T”. This advantage is reinforced by the presence of the angled or knife elements. These angled elements, which are staggered in relation to the angled elements of a neighbouring bar, are used, during the relative movements of the bars in relation to each other, to cut any particles that might accumulate between the bars.

The shape of the front end of the bar, in particular with the presence of the fin for redirection of the air coming from the passages formed by the lateral hollow-outs, to a channel located in the top part of the front end of the bar, results in efficient blowing of the oxidising air, at the surface of the flat part, toward the rear end of the bar, and therefore of the grate, so that the air is blown in the direction of removal of the products.

The angle of attack of the front end of the bar prevents the accumulation of particles at this point and therefore the lifting of the bar.

All these advantages therefore considerably reduce the risk of blocking the relative movements of the bars, since these movements are essential for efficient removal of the particles, which must not be pushed to the outside, as well as for effective and well distributed combustion on the grate.

These limited relative movements are rendered possible and controlled by means of a dowelling or pinning technique.

Other characteristics and advantages of the invention will appear more clearly and more completely on reading the description that follows of the preferred variants of implementation of the system, which are given by way of non limiting examples and with reference the following appended drawings.

FIG. 1 schematically represents a set of three bars according to the invention, in cross section,

FIG. 2 schematically represents a portion of a bar according to the invention, in perspective,

FIG. 3 a schematically represents a portion of a bar according to the invention, as seen from the side,

FIG. 3 b schematically represents a portion of a bar according to the invention, as seen from above and in perspective,

FIG. 4 schematically represents the front end of a bar according to the invention, as seen from the side,

FIG. 5 a schematically represents a grate formed from several bars assembled according to the invention, as seen from below,

FIG. 5 b schematically represents a detail of the assembly of three bars according to the invention, as seen from below.

FIG. 1 schematically represents a set of three bars according to the invention, in cross section.

Three bars 1, 9, 13 are represented in this figure. It can be seen that the main section of each bar has the shape of “T” with, in the case of bar 1, a flat part 3 that surmounts a longitudinal projection 6. This main section, in the shape of a “T”, offers, amongst other advantages, an optimised level of geometrical and mechanical precision, and a good resistance to high-temperature deformations, due to its moment of inertia.

The material used is preferably a refractory alloy that offers high resistance to abrasion when hot, to corrosion when hot, to oxidation, and to thermal shock. A method of manufacture by casting allows the implementation of such highly alloyed and refractory alloys. The main section, in the shape of a “T”, which is totally removable from its mould, allows the use of a “natural” casting method that has the particular advantage of being comparatively more convenient than other methods of casting that are more complex.

Under the flat part 3, a first wing 7 is positioned on a first side 6 a of the longitudinal projection 6, and a second wing 11 can be positioned on another side 6 b of this longitudinal projection 6. The wings 7, 11 respectively have lateral hollow-outs 7 a, 11 a. The adjoining bars 9, 13 also respectively have wings 8, 12. Wing 8, which is opposite to wing 7 of bar 1, has a lateral hollow-out 8 a that is opposite to the lateral hollow-out 7 a of wing 7 of bar 1. Wing 12, which is opposite to wing 11 of bar 1, has a lateral hollow-out 12 a that is opposite to the lateral element 11 a of wing 11 of bar 1.

Thus, a passage 10 is formed between bar 1 and bar 9, and a passage 14 is formed between bar 1 and bar 13. The position of the lateral hollow-outs in the wings, meaning the top corner oppose to the longitudinal projection of the bar to which each wing belongs, precisely allows the creation of passages just below the respective flat parts of the bars. The purpose of these passages is to channel the air up to the front end of each bar.

FIG. 2 schematically represents a portion of a bar according to the invention, in perspective.

In bar 1 represented also in FIG. 2, we find the flat part 3 and the longitudinal projection 6. A bar 1 extends to a front end 5 forming a return that acts as a support point in the case of bar 1. This figure also shows that the longitudinal projection 6 actually extends under the flat part 3 from the front end 5 in the direction of the rear end (not shown). It could possibly extend only partially under the flat part 3 between the front end and the rear end.

On one side 6 a or on each side 6 a, 6 b of the longitudinal projection 6, several wings can be positioned, namely wings 7, 7′ and 7″ on a first side 6 a, and wings 11, 11′ and 11″ on the other side 6 b. Wings 7, 7′ and 7″ respectively have lateral hollow-outs 7 a, 7 a′, 7 a″. Wings 11, 11′, and 11″ respectively have lateral hollow-outs 11 a, 11 a′, 11 a″, which are shown only partially due to the perspective view.

The succession of lateral hollow-outs on each side of the longitudinal projection 6, in combination with the succession of lateral hollow-outs in the adjoining bars (not shown in FIG. 2), form on each side of this longitudinal projection 6, and between bar 1 and its adjoining bars, a channel for guiding the air up to the front end 5.

The number of these wings on each side of the longitudinal projection 6 does not limit the invention of course, since bar 1 is not shown over all of its length. The number of these wings will depend essentially on the length of bar 1. In fact, this is an important parameter for accelerating the cooling of bar 1.

In this figure, wings 7, 7′ and 7″ and 11, 11′, 11″ are represented perpendicularly to the longitudinal projection 6 and slightly inclined in relation to the flat part 3, at the rear end (not shown) of bar 1. This position is only an example however and does not limit the invention. In fact, these wings could just as well be positioned in an inclined manner, to the rear for example, in relation to the longitudinal projection 6, and perpendicularly to the flat part 3. The position in the example of FIG. 2 nevertheless gives good results in relation to the objective sought, namely cooling of bar 1 by the oxidising air running between the wings.

The arrows shown in FIG. 2 symbolise the circulation of this oxidising air between the wings, in order to favour cooling of the bar.

In addition, FIG. 2 also shows angled elements 15, 15′, 15″ at the side 6 a of the longitudinal projection 6, under the flat part 3. Here again, the number and the position of these angled elements places no limitation on the invention. An appropriate position is one that results in an effective ability to cut any particles between an angled element of one bar and an angled element of a neighbouring bar.

A bar 1 can also have one or more of these angled elements on the other side 6 b of this longitudinal projection 6, which are not visible here due to the perspective view.

These angled elements, which therefore act in the role of knives are positioned in a staggered manner in relation to the angled elements of a neighbouring bar (not shown in FIG. 2). The result is that, during the relative movements of the bars in relation to each other, they cut any particles that might accumulate between the bars.

FIG. 3 a schematically represents a portion of a bar according to the invention, as seen from the side.

It highlights the inclination of wings 7, 7′ and 7″ under the flat part 3, to the rear end (not shown and inverted in relation to FIG. 2), and perpendicularly to the longitudinal projection 6. The lateral hollow-outs 7 a, 7 a′, 7 a″ are also represented.

The angled elements 15, 15′, 15″ are shown by solid lines, and the angled elements on the other side of the longitudinal projection 6 and/or of a neighbouring are shown by broken lines (but not referenced).

FIG. 3 b schematically represents a portion of a bar according to the invention, as seen from below and in perspective.

It highlights the distribution of the angled elements on each side of the longitudinal projection 6, in one particular embodiment. In the latter, the angled elements are positioned precisely under the flat part 3, against and perpendicularly to the bottom surface 3 b of this flat part 3. They are distributed on each side of the longitudinal projection 6, respectively against and perpendicularly to the sides of this longitudinal projection 6.

FIG. 4 schematically represents the front end of a bar according to the invention, as seen from the side.

The front end 5 of the bar forms a return whose base 5 a acts as a support point for the bar. This base 5 a has an attack angle α that is greater than 0°. Thus, during the movements in longitudinal translation of the bars in relation to each other, this angle of attack prevents the accumulation of particles under the front end 5 of the bar and therefore the lifting of this bar.

Preferably, an effective angle of attack will be between 2° and 10°. A particularly good result is achieved with an angle of attack that is more-or-less equal to 3°.

On one side, or on each side, of the longitudinal projection 6, this front end 5 of the bar also has a fin 16 for redirection of the air (the redirection being symbolised by the upwardly-pointing arrow) coming from the passages formed by the lateral hollow-outs in the wings (not shown) along the longitudinal projection 6. The internal curved shape of this fin 16 actually favours the redirection of the air. This air is redirected to a channel 18, on one side, or on each side, of the longitudinal projection 6. This channel 18 starts at the bottom surface 3 b of the flat part 3, perpendicularly to this flat part 3. It then emerges at the top of the top surface 3 a of the flat part 3, parallel to this flat part 3. The air exiting from this channel 18 is symbolised by the arrow in the direction of the rear end (not shown) of the bar.

This channel 18 can have a circular section, possibly with an input diameter, meaning at the bottom surface 3 b of the flat part 3, that is greater than its output diameter, meaning at the top of the top surface 3 a of the flat part 3.

Thus, the oxidising air is blown in an optimised manner to the rear, meaning in the direction of removal of the products.

FIG. 5 a schematically represents a grate formed from several bars assembled according to the invention, as seen from below.

In this figure, grate 2 includes two groups 20, 20′ each of three bars, 1, 9, 13 and 1′, 9′, 13′ respectively. In each of these groups, the central bar 1 or 1′ is mobile in relation to the lateral bars 9, 13 or 9′, 13′ which remain fixed. The movements of these central bars 1, 1′ relatively to their respective adjoining bars 9, 13 and 9′, 13′ are symbolised by arrows in the direction of the longitudinal axis of the bars, in both directions.

Assembly of the bars in each group is effected by means of a dowelling or pinning technique 21, 22, 23 for group 20, highlighted in the circled zone D, which will be described in greater detail with reference to FIG. 5 b, and 21′, 22′ and 23′ for group 20′.

FIG. 5 b therefore schematically represents zone D of the assembly of the three bars 1, 9, 13 of group 20 in FIG. 5 a, as seen from below.

Assembly is effected at the front ends of the bars by means of a dowelling or pinning technique that include a threaded axial rod 21 and two locking pins or dowels, one 22 at the level of a first lateral bar 9 with a right-hand thread, and the other 23 at the other lateral bar 13 with a left-hand thread. The round heads of the pins 22, 23 (the head of pin 22 is referenced 24 in FIG. 5 a) each have a locking flat part (reference 25 for pin 22 in FIG. 5 a), and each fits into a circular housing (reference 26 for head 24 of pin 22 in FIG. 5 a) provided in the longitudinal projection of each bar 9, 13, with these circular housings each also having a locking flat part. The role of these locking flats is in fact to lock the bars, both in rotation about the axis of the rod 21, and in translation of one neighbouring bar 9 in relation to the other neighbouring bar 13.

In addition, the circular housings in the longitudinal projection of each bar have a longitudinal extension at the rear in the form of a groove 27 of sufficient width to allow the passage of the rod 21.

Thus, this assembly system by means of a dowelling or pinning technique provides for the freedom in translation of the central bar 1, 1′ in each group 20, 20′, between two extreme positions, in relation to the two lateral bars 9, 13 and 9′, 13′ respectively. In fact the travel in translation of the central bars 1, 1′ is limited by the length of the groove 27.

Thus, the limited translation movement described above, which is essential for efficient removal of the particles, which must not be pushed to the outside, as well as for effective and well distributed combustion on the grate, is rendered possible and controlled by the assembly system just described.

All of the description above is given by way of an example, and does not limit the scope of the invention. 

1. A bar for a grate in the firebox of an incineration furnace that includes: a flat part whose top surface is intended to receive the elements to be incinerated, with the said flat part extending in a rear end and a front end each forming a return that acts as a support point for said bar, a longitudinal projection located under said flat part and that extends at least partially between said rear and front ends, at least one wing positioned under said flat part, on a first side of said longitudinal projection, wherein said wing extends from said longitudinal projection up to the bottom surface of said flat part and is provided with at least one lateral hollow-out bordered at the top at least partially by said bottom surface of said flat part, so that this lateral hollow-out, together with the lateral hollow-out of a wing of a first adjacent bar of said bar, forms a passage for channelling the air just below said flat part and up to said front end of said bar.
 2. A bar according to claim 1, further comprising at least one second wing that extends from said longitudinal projection up to the bottom surface of said flat part and that is positioned under said flat part, on a second side of said longitudinal projection, with said second wing being provided with a lateral hollow-out bordered at the top at least partially by said bottom surface of said flat part and, together with the lateral hollow-out of a wing of a second adjacent bar of said bar, forming a second passage for channelling the air just below said flat part and up to said front end of said bar.
 3. A bar according to claim 1, further comprising a multiplicity of wings distributed under said flat part along said longitudinal projection, on a first side or on each side of said longitudinal projection, with said wings extending from said longitudinal projection up to the bottom surface of said flat part and being provided with respective lateral hollow-outs outlined at the top at least partially by said bottom surface of said flat part, which, together with the respective lateral hollow-outs of the wings of the adjacent bar or bars of said bar, form passages, these said passages forming, on said first side or on each side of said longitudinal projection, a channel for guiding the air just below said flat part and up to said front end of said bar.
 4. A bar according to claim 1, further comprising at least one angled cutting element located under said flat part, on a first side of said longitudinal projection.
 5. A bar according to claim 1, further comprising a multiplicity of angled cutting elements distributed under said flat part, on a first side or on each side of said longitudinal projection.
 6. A bar according to either of claim 4, wherein each of said angled cutting elements is located firstly against the bottom surface of said flat part and perpendicularly to this bottom surface, and secondly against one or other side of said longitudinal projection and perpendicularly to this side.
 7. A bar according to claim 1, wherein the base of said front end of said flat part has an attack angle that is greater than 0°.
 8. A bar according to claim 7, wherein said attack angle is between 2° and 10°.
 9. A bar according to claim 1, wherein said front end of said flat part is provided, on at least one of the sides of said longitudinal projection with a fin for redirection of the air coming from said passage or passages, to at least one channel located in the top part of said front end of said flat part.
 10. A bar according to claim 9, wherein said channel starts at the bottom surface of said flat part and perpendicularly to said flat part, and opens out onto the top of the top surface of said flat part, parallel to said flat part.
 11. A grate for the firebox of an incineration furnace, wherein the grate includes at least one bar according to claim
 1. 12. A grate for the firebox of an incineration furnace, wherein the grate includes at least one group of three bars according to claim 1, with the central bar in said group being mobile in relation to the two lateral bars in said group.
 13. A grate according to claim 12, wherein said bars in at least one of said groups are assembled by means of a dowelling or pinning technique that locks the two lateral bars in relation to each other, and that leaves the central bar free in translation, between two extreme positions, in relation to the two lateral bars.
 14. A bar according to claim 5, wherein each of said angled cutting elements is located firstly against the bottom surface of said flat part and perpendicularly to this bottom surface, and secondly against one or other side of said longitudinal projection and perpendicularly to this side. 